In Australia, residential areas are often made of large contiguous fenced lots with a house in the middle of each.

Would you say that an OSM mapper should prioritise mapping the contiguous lots or rather the house itself, taking into account that the lots are probably the areas that will change less frequently over time?

But in general, we have seen that buildings are mapped first (after roads), most probably because it's more visible from the ground and from the aerial imagery. A lot is not always fenced then you might have areas with buildings only and areas with fences only...

And generally, we don't like to see parcels in OSM, especially when they are virtual. And it's not true that parcels are more stable than buildings, they are constantly changing with merges and splits. Synchronizing them in OSM would be a huge task as well.